1. Field of the Invention
The present invention relates to a method which is directed to the fabricating or forming of tubular members of the torque tube type which may be utilized as torque joints for the drive shafts or steering connections of motor vehicles or in connection with articulating linkages for high-lift aircraft systems, marine systems or for other various military or non-military commercial physical application where it is intended to react to torsional and axial loads which are ordinarily encountered in torque joints, steering linkages, drive shafts and the like. More particularly, pursuant to a further aspect of the invention, provision is made for a device which is in the form of a novel die arrangement for electromagnetically forming spirally oriented grooves in tubular members and therewith interposed end fittings, particularly of the type which are adapted to react to intense torsional and axial loads encountered by torque joints and the like, and which are designed to appreciably reduce or even essentially eliminate stress concentrations so as to improve upon the fatigue life and, resultingly, extend the service life or durability of the torque tube assembly.
In essence, it is a well-known and common procedure in industrial applications to form grooves in tubes and conjoint end fittings which are to be utilized in the fabrication of torque joints or torque tube assemblies employed for drive shafts and the like in order to be able to react to torsional and axial loads which are encountered in the drive shafts. Heretofore, such grooves were generally produced by machining the tubular members in a labor-intensive and time-consuming manner, thereby rendering the entire process of their manufacture expensive and not particularly economically viable.
2. Discussion of the Prior Art
Pursuant to the more recent state of the technology which is employed in the manufacture of so-called conformal torque tube joints incorporating grooves in both longitudinal and circumferential orientations in order to produce a torque joint of interlockingly conformed tubular members, the end fitting and the tube section located thereon or therein were normally joined together by concurrently forming torque-reacting grooves over an internal shaped die member or mandrel so as to eliminate the necessity for machining the grooves in the end fitting.
For example, a method of fabricating a torque joint incorporating longitudinal or axial grooves and also providing for circumferentially extending or radial grooves may be ascertained in Arena U.S. Pat. No. 4,513,488 which enable the transmission of forces or loads in both longitudinal or circumferential directions through the intermediary of thin-walled and resultingly lightweight tubular torque tubes. In that instance, an inner tube and an outer tube are overlapped, a mandrel possessing longitudinal and circumferential grooves or ridges inserted therein, and an externally applied and radially inwardly directed deformation force compresses the tubular members into the grooves or between the ridges in the mandrel, subsequent to which the mandrel or at least the inserted portion of the mandrel is extracted to then provide the formed torque tube joint.
In Arena, et al. U.S. Pat. No. 4,523,872, there is disclosed a torque tube employing end members interconnected by means of a tubular member, wherein the end members are provided with a male extension having radially spaced, axially extending grooves, with the number of grooves, outer diameter of each end member, groove width and groove length being in prescribed proportions and ratios. The ends of the tubular member are positioned over the male end member extension and the tube walls conformed to the end member and grooves through the external application of electromagnetic energy so as to cause the tube walls to be recessed or radially inwardly compressed into the grooves.
Various methods and apparatus describing the formation of grooves in tubular members in either mechanical or electromagnetic modes, particularly such as for the formation of torque joints and the like which are suitable for diverse physical and mechanical applications are disclosed in Suh, et al. U.S. Pat. No. 4,397,171; Ohki U.S. Pat. No. 4,598,451; Queyroix U.S. Pat. No. 3,810,372; Grob U.S. Pat. No. 4,125,000; Clements U.S. Pat. No. 2,233,471; Savon U.S. Pat. No. 1,329,479; and Bright, et al. U.S. Pat. No. 1,291,388.
Each and every one of the foregoing patents, although disclosing the formation of grooves in tubular members, for example, such as for the formation of torque joints for drive shafts, aircraft control linkages, and the like, disclose either mechanical devices for compressing the tubular material, and/or electromagnetic force-generating devices which are normally externally applied so as to form longitudinal and circumferential grooves, or devices generating internal electromagnetic forces in cooperation with external dies so as to provide longitudinally extending grooves in tubular members.
More recently, torque tube joints of the type described hereinabove, and which possess both longitudinal and circumferential grooves, have been formed through the application of electromagnetic forces produced by internal coils and with external die structure having either radially inwardly depending raised ridges or groove-like recesses formed in the tube-encompassing bores thereof so as to facilitate expansion of the superimposed tubular members within the bores to produce conformal longitudinal and circumferential grooves therein. Although the outwardly expansive deformation rather than radially inwardly directed compressive forces applied to the tube member material enables the formation of conformal torque tube joints which facilitates reaction to the applications of greater forces onto the torque tube joints, the formation of axially and radially oriented grooves in the torque joints is subject to physical limitations. Thus, in current designs when a drive shaft or torque tube joint is highly (operatively) loaded, the material thereof normally tends to react the applied torque in a generally spiral direction. Consequently, as can be demonstrated through structural testing, when a tubular member is loaded statically in torsion, the material reaches a point at which the tubular member may fail by torsional buckling or by the shearing of the metal, or through a tensile stress failure of the tube material. Such tubes generally exhibit a deformation which assumes a spiral appearance, and in a similar manner when a torque tube of conventional design; in effect, possessing axially and radially extending grooves, is tested for fatigue by a repetitive application of torque loads in alternating opposite directions, the tube will generally fail at the beginning or the end of the axially oriented grooves. The reason for this failure may be found in that the groove which is aligned axially and the material of the tube have a tendency to align themselves in a spiral pattern in order to react the torsional loads applied thereto, and the transition between the end of the axial groove and the tube material itself creating a stress concentration which generates a weak link in the torque tube assembly, thereby reducing its fatigue life and, consequently, its useful service life.
In order to ameliorate or even obviate the above-mentioned problem by forming the grooves in the tubular members in a spiral orientation, the grooves are essentially positioned in an optimized pattern so as to efficiently react any forces imposed on the torque tube and, resultingly, eliminate or reduce any adverse stress concentrations to impart superior properties and improvements in comparison with current state-of-the-art torque tube assemblies.